To calibrate an optical system, it can often be desirable to measure the system's point spread function and evaluate the system's spectral radiometric response to small targets. For optical systems that include a color filter mosaic disposed on an array of sensor pixels, it can be difficult to directly measure such a point spread function. If such a measurement uses signals from just red pixels, just green pixels, or just blue pixels on a multi-wavelength detector, the signals may include holes or gaps, due to the non-contiguous nature in which the red pixels, green pixels, or blue pixels are arranged on the detector. The result is to spatially undersample the scene content in each spectral band.